Aircraft deicing systems are well-known and widely used saftey devices for the removal of ice accumulated on aerodynamically significant aircraft surfaces, such as propeller and helicopter rotor blade airfoils. It has been found that cycling the application of heat to the airfoil radially outwardly from root to tip of a rotating airfoil results in substantially improved ice shedding characteristics with significantly reduced energy requirements. Accordingly, most present-day aircraft deicing systems incorporate a plurality of electrical resistance-type heating elements, known as deicing segments, which are sequentially and cyclically energized in symmetrical pairs on opposing blades.
In order to selectively energize each deicing segment, a separate electrical connection was necessary for each opposing pair of deicing segments and a single additional electrical connection, common to all deicing segments, was required to complete each two-wire deicing segment circuit. Unfortunately, the energy requirements of these deicing segments are such that power must be obtained from one of the electrical power generator's located elsewhere on the aircraft. Thus, some mechanism is required for coupling the power from the aircraft's fixed generating system to the rapidly rotating propeller or rotor blades. Heretofore a suitable plurality of brush block assemblies were rigidly mounted to the aircraft, and slip-ring assemblies positioned on the rotating propeller or rotor drive shaft to effectuate this coupling. For example, in a helicopter with six deicing segments on each of four main rotor blades and a single deicing segment on each of two tail rotor blades, provided pairs of segments on opposing blades are simultaneously energized, a total of 13 slip-ring asssemblies for the main rotor blades and 2 slip-ring assemblies for the tail rotor blades were required. However, such assemblies are subject to substantial wear, require frequent maintenance and replacement and, because of the large number of assemblies required, present a constant threat of in-flight deicing system failure.
I am specifically aware of only one other control system for the cyclic distribution of D.C. electrical power to deicer elements on rotating propeller blades in which the number of required slip-ring assemblies is minimized, my previous invention, U.S. Pat. No. 3,657,514. However, the nature of that control system is such that its use is limited to selectively controlling only two sets of deicing segments, unlike the unlimited number that may be selectively controlled by the present invention, as detailed hereinafter.
Other deficiencies of the prior art deicing systems includes the inability to provide rapid testing of the deicing system when the aircraft is resting on land (and air cooling capabilities are limited), continual visual monitoring of the deicing system operational status, and a simple mechanism for the adjustment of deicer segment heating cycle times.